1. Technical Field
The present invention generally relates to wireless communication systems and in particular to a combination of multiple input, multiple output and beamforming (MIMO+BF) using a single antenna sounding from a mobile station (MS).
2. Description of the Related Art
In a Worldwide Interoperability for Microwave Access (WiMAX) mobile system, an option exists to provide for the transmission in a two-antenna Space Time Coding (STC) zone using dedicated pilots (hereinafter referred to as a “STC option”). The STC option allows for the use of beamforming in conjunction with a multiple input, multiple output (MIMO) downlink (DL) transmission to provide both coverage and capacity benefits over the use of either technique separately. In the STC operating mode, the base station (BS) would form two beams that essentially create “virtual” antennas over which MIMO Matrix A or MIMO Matrix B transmission can be performed. Unfortunately, to support such a transmission technique, the WiMAX profile supports uplink channel sounding (ULCS) from only one of the subscriber antennas, thereby precluding the conventional closed-loop MIMO schemes (e.g. MIMO schemes based on the singular value decomposition (SVD) of the channel matrix).
The WiMAX profile and others describe a broad idea of MIMO+BF in a closed-loop (CL) MIMO system with a single antenna sounding. Some suggest that CL-MIMO does not work with knowledge to only one receive antenna. In one example, the WiMAX R1W2 profile allows for the combination of MIMO and beamforming by permitting MIMO Matrix A/B transmission with dedicated pilots. In another example, the WiMAX R1W2 profile contains an up link channel sounding (ULCS) from only one mobile station (MS) antenna. The base station (BS) learns the channel to only one of the MS's RX antennas. However, it would be desirable to provide closed-loop Spatial Multiplex MIMO transmission with knowledge of a M-by-1 (where M represents the number of BS antennas, M>1) downlink (DL) channel and that computes the transmit weights for such closed-loop MIMO transmissions.
Within the descriptions of the figures, similar elements are provided similar names and reference numerals as those of the previous figure(s). Where a later figure utilizes the element in a different context or with different functionality, the element is provided a different leading numeral representative of the figure number (e.g., 1xx for FIG. 1 and 2xx for FIG. 2). The specific numerals assigned to the elements are provided solely to aid in the description and not meant to imply any limitations (structural or functional) on the invention. It should be understood that the use of specific component, device and/or parameter names are for example only and not meant to imply any limitations on the invention. The invention may thus be implemented with different nomenclature/terminology utilized to describe the components/devices/parameters herein, without limitation. Each term utilized herein is to be given its broadest interpretation given the context in which that terms is utilized.